Remote conductivity sensor using square wave excitation

Abstract

A liquid conductivity sensor which features simply and inexpensively driving the excitation transformer of a two-transformer/fluid-loop remote conductivity sensor with a square wave excitation signal provided by a digital timer and a flip-flop. Also disclosed is using an electrodeless conductivity sensor to sense conductivity of dialysate.

What is claimed is: 
     
       1. Apparatus for remotely sensing conductivity of a fluid passing through it, said apparatus comprising a cell including means for defining a fluid flow path having a fluid loop and excitation and sensing transformers each having a core encompassing a portion of said fluid loop, and   a digital timer and a flip-flop connected to provide a square wave excitation signal to said excitation transformer.   
     
     
       2. The apparatus of claim 1 wherein said excitation transformer is bifilar wound and is connected to both the true and complement outputs of said flip-flop. 
     
     
       3. The apparatus of claim 1 further comprising a current-to-voltage converter connected to said sensing transformer. 
     
     
       4. The apparatus of claim 3 further comprising an AC amplifier connected to said current-to-voltage converter. 
     
     
       5. The apparatus of claim 1 further comprising a turn about said excitation transformer and a turn about said sensing transformer for use in calibrating said apparatus. 
     
     
       6. The apparatus of claim 4 further comprising a synchronous detector connected to said digital timer and to said AC amplifier, said detector providing a DC voltage output. 
     
     
       7. The apparatus of claim 6 further comprising a turn about said excitation transformer and a turn about said sensing transformer for use in calibrating said apparatus. 
     
     
       8. The apparatus of claim 7 wherein said excitation transformer is bifilar wound and is connected to both the true and complement outputs of said flip-flop. 
     
     
       9. Dialysate preparation and supply apparatus comprising a dialysate supply line,   fluid flow path means for defining a fluid flow path in said supply line, said means having an inlet and an outlet and two fluid paths between the two, thereby defining a fluid loop,   an excitation transformer comprising a first toroidal core having a hole through it and wire turns around it, said core encompassing a portion of said fluid flow path means and said fluid loop therein,   a sensing transformer comprising a second toroidal core having a hole through it and wire turns around it, said core encompassing a portion of said fluid flow path means and said fluid loop therein, and   a digital timer and a flip-flop connected to provide a square wave excitation signal to said excitation transformer.   
     
     
       10. Dialysate preparation and supply apparatus comprising a dialysate supply line,   fluid flow path means for defining a fluid flow path in said supply line, said means having an inlet and an outlet and two fluid paths between the two, thereby defining a fluid loop.   an excitation transformer comprising a first core having a hole through it and wire turns around it, said core encompassing a portion of said fluid flow path means and said fluid loop therein,   a sensing transformer comprising a second core having a hole through it and wire turns around it, said core encompassing a portion of said fluid flow path means and said fluid loop therein, and   a digital timer and a flip-flop connected to provide a square wave excitation signal to said excitation transformer.